The Chemistry of the Binuclear 34-Electron System [C₅R₅M(μ-PMe₂)]₂: How Inert Are M-PMe₂-M Bridges?

Abstract

The binuclear cobalt and rhodium complexes, [C₅H₅Co(μ-PMe₂)]₂ (1) and [C₅Me₅Rh(μ-PMe₂)]₂ (2), behave as metal bases and react with electrophiles by addition to the metal-metal bond. Whereas with acids such as CF₃CO₂H cations of general composition [(C₅R₅M)₂(μ-H)(μ-PMe₂)₂]⁺ which still show a strong M-M interaction are formed, the reaction with CH₂X₂ (X = Br, I) leads to M-M bond cleavage and insertion of CH₂ into one of the M-PMe₂-M bridging bonds. The chalcogens (O, S, Se and Te) and activated alkynes RC≡CCO₂Me (R = H, Me, CO₂Me) behave similarly. The essence of this Comment is that M-PMe₂-M bridges are less rigid than originally expected and in various cases play a specific role in reactivity.

Key Words:

• dimethylphosphido-bridged cobalt and rhodium complexes
• addition of electrophiles
• insertion reactions
• bimetallic initiated template synthesis